Apparatuses using electric motors, such as hybrid automobiles and electric automobiles, use power conversion devices to save energy. Such power conversion devices typically use a semiconductor module. The semiconductor module constituting a control device serving to save energy is provided with a power semiconductor element that controls a large electric current. The usual power semiconductor element generates heat when a large electric current is controlled, and the amount of the generated heat increases with the miniaturization and increase in output of the power conversion device. Therefore, in a case of a semiconductor module provided with a plurality of power semiconductor elements, cooling the semiconductor module is a significant problem.
Cooling devices of a liquid cooling system have been used as cooling devices to be attached to semiconductor modules in order to cool the modules. Such a cooling device of a liquid cooling system is provided with a heat radiation substrate that is made from a metal and joined to an insulating substrate carrying the power semiconductor elements on the side thereof opposite that where the semiconductor module is disposed, heat radiation fins formed integrally with the heat radiation substrate, and a box-shaped cooling case that accommodates the fins and is liquid tightly attached to the heat radiation substrate. An introducing port and a discharge port for a cooling medium (cooling liquid) are connected to the cooling case. A flow path is formed inside the cooling case for the cooling medium introduced into the cooling case from the introducing port to pass through the fins and be discharged from the discharge port. The cooling medium (for example, water or a long-life coolant) pressurized by an external pump is introduced from the introducing port and flows through the flow path inside the cooling case. As a result, the thermal energy generated by the power semiconductor elements is released through the fins to the cooling medium. The cooling medium is discharged from the discharge port, cooled in an external heat exchanger, pressurized by the pump, and then returned into the flow path inside the cooling case.
A cooling device of such type is known in which an inlet and an outlet for a cooling medium are provided at the longitudinal ends of the cooling device, fins provided correspondingly to a plurality of semiconductor modules are arranged along the longitudinal direction of the cooling device in the flow path inside the cooling device between the inlet and outlet, and a cooling medium is brought into direct contact with the fins (Patent Document 1, identified further on). In the cooling device described in Patent Document 1, the inlet and outlet for the cooling medium are provided at the rear surface of a heat sink, in other words, at the bottom surface of the cooling device.
A variety of measures have been taken to increase the cooling efficiency of the cooling device of a liquid cooling system. Thus, it has been suggested to increase the flow rate of the cooling medium, provide the heat-radiating fins (cooling bodies) in the cooling device with a shape ensuring good thermal conductivity, and use materials with a high thermal conductivity to configure the fins.
For example, a cooling device has been suggested in which a wall for enhancing the diffusion of a cooling medium is provided between an inlet portion and a cooling medium passage (Patent Document 2, identified further on). A cooling device has also been disclosed in which a groove or a protrusion for diffusing a coolant is provided between the inlet and outlet of the cooling device (Patent Document 3, identified further on). A cooling device has also been suggested in which an introducing tube and a discharge tube for a cooling agent are provided in the vicinity of the corner portion of the circumferential end on the longitudinal end side of a radiator, and a columnar member is provided between the introducing tube and discharge tube (Patent Document 4, identified further on). A cooling device has also been disclosed in which heat radiation protrusions are provided in a rectangular base portion (except for the corners thereof) integrated with a circumferential wall portion, an inflow port and an outflow port for a cooling medium are provided in a lower lid provided opposite the tips of the heat radiation protrusions, the turbulence of the cooling medium in the corners of the base portion is enhanced and cooling efficiency is increased (Patent Document 5, identified further on).
Patent Document 1: Japanese Patent Application Publication No. 2001-308246 (see paragraph [0018] and FIG. 1)
Patent Document 2: Japanese Patent Application Publication No. 2007-123607 (see claims and paragraph [0041])
Patent Document 3: Japanese Patent Application Publication No. 2005-19905 (see claims and FIG. 1)
Patent Document 4: Japanese Patent Application Publication No. 2007-294891 (see paragraph [0017])
Patent Document 5: Japanese Patent Application Publication No. 2011-103369 (see paragraph [0031] and FIG. 1)
In the cooling device described in Patent Document 1, the flow rate of the cooling medium flowing inside the cooling device is large in the lateral central portion of the flow path thereof and small on the periphery thereof. Therefore, there is a difference in the degree of cooling between the semiconductor elements disposed close to the lateral center of the flow path of the cooling medium flowing in the cooling device and the semiconductor elements disposed on the periphery. In this regard, where a wall, a groove, or a protrusion for enhancing the diffusion of the cooling medium is provided, as described in Patent Documents 2 to 5, the spread of the flow rate in the lateral direction of the passage can be suppressed and the difference in the degree of cooling of the semiconductor elements can be suppressed.
However, the demand for increased heat radiation ability of cooling devices continues to grow, and the heat radiation ability needs to be increased as the power conversion devices are reduced in size and increased in power.
Further, in the cooling devices described in Patent Document 1 and Patent Document 5, the inlet and outlet of the cooling medium are provided in the bottom surface of the cooling device. As a result, no electronic component, such as a film capacitor, can be attached to the bottom surface of the cooling device.